1. Field of the Invention
The present invention relates to a battery, and more particularly, to a cap assembly of a battery having an improved structure which can be electrically disconnected from other parts when a safety member is ruptured due to the accidental internal pressure increase of the battery.
2. Description of the Related Art
As portable appliances such as video cameras, mobile phones and portable computers become lighter and more versatile, research has been concentrated on batteries to power such appliances. Among conventional batteries, a lithium secondary (i.e. rechargeable) battery has about 3 times the energy density per unit weight of conventional batteries such as a lead acid battery, a Ni-Cd battery, and a Ni-H battery, and can be fast charged. In the lithium secondary battery, lithium cobalt oxide (LiCoO.sub.2), lithium nickel oxide (LiNiO.sub.2), lithium manganese oxide (LiMn.sub.2 O.sub.4) or the like is used as an active material of a positive electrode, and lithium, lithium alloys, a carbon material or the like is used as an active material of a negative electrode. In addition, organic electrolyte or solid polymer electrolyte is used as an electrolyte. In general, the shape of a secondary battery is cylindrical or rectangular, and the rectangular shape is advantageous to making the portable appliances light and small.
Referring to FIG. 1, a conventional lithium secondary battery of a rectangular shape comprises a battery case 17 for accommodating an electrode core (not shown) which is alternately laminated with positive electrode plates and negative electrode plates having separators therebetween, and a cap assembly 10 attached to the upper portion of the battery case 17.
The cap assembly 10 includes a cap plate 12 for covering the upper portion of the battery case 17, a positive terminal 11 installed on the cap plate 12, and a rivet member 15 inserted through holes formed in the positive terminal 11 and the cap plate 12, for joining the positive terminal 11 to the cap plate 12. A first insulating member 13 is interposed between the positive terminal 11 and the cap plate 12, and the cap plate 12 and the rivet member 15 are insulated from each other by a second insulating member 14.
A positive tap 16 which is connected to the positive electrode plates (not shown) is welded to the rivet member 15. In addition, the battery case 17 is connected to a negative tap (not shown).
An electrolyte injection hole 12a for injecting an electrolyte into the battery case 17 is formed at one side of the cap plate 12, and a rupturing portion 12b is formed at the other side of the cap plate 12, to rupture when the internal pressure of the battery is abnormally high.
When the internal pressure of the lithium secondary battery is abnormally high, the rupturing portion 12a of the cap plate 12 ruptures, and gas within the battery is exhausted. At this time, since the battery is still electrically connected, and has no electrical safety means, the portable appliance in which the battery is used may suffer a subsequent accident such as an electrical shock.